CN116184117A - Cable local defect positioning method, system, equipment and medium - Google Patents

Abstract

The invention discloses a cable local defect location method, system, equipment and medium. The method includes: using the frequency domain reflection spectrum to locate the cable local defect, and obtaining the location result; wherein, using the frequency domain reflection spectrum to locate the cable local defect When performing positioning, during the acquisition process of the kernel function in the high-voltage cable local defect localization spectrum function based on the integral transformation method of the generalized orthogonal theory, the resistance per unit length of the cable body and the inductance per unit length of the cable body are calculated by the finite element method It is obtained by combining with the analytical calculation method; the conductance per unit length of the cable body and the capacitance per unit length of the cable body are obtained by establishing a layered model of the cable insulation medium considering the semiconductive layer. The invention specifically discloses a new method for obtaining a local defect localization kernel function of a cable, which can obtain an accurate localization kernel function and finally improve the local defect localization accuracy of the cable.

Description

A method, system, device and medium for locating local defects in a cable

Technical Field

The present invention belongs to the technical field of cable fault detection, and in particular relates to a method, system, equipment and medium for locating local defects of a cable.

Background Art

Cables (for example, high-voltage cables; high-voltage cables are a type of power cable, generally referring to power cables used to transmit power between 1kV and 1000kV, mostly used in power transmission and distribution) are key power equipment in urban transmission networks, and play an extremely important role in smart grids and UHV projects. Cables may have various latent insulation defects during the production process, and will also be affected by various factors after being put into operation. The combined effect of the above factors makes the cables prone to various faults, which will affect the safe and stable operation of the power system. In summary, how to quickly and accurately detect faults and determine the fault location is the key issue facing cable operation and maintenance at this stage.

In addition, in recent years, a new type of cable fault has appeared in XLPE insulated corrugated aluminum sheathed cables with voltage levels of 110kV and above in many places at home and abroad. The fault location is not the high-voltage cable accessories or the main insulation, but between the metal shielding layer and the insulating shielding layer of the high-voltage cable, that is, the buffer layer defect. Using traditional cable fault detection methods (such as state detection technology based on electrical parameters such as cable breakdown voltage, dielectric loss, leakage current, insulation resistance, etc., withstand voltage testing, partial discharge monitoring technology, time domain reflection method, etc.), it is impossible to detect such latent defects. Explanatory, high-voltage cables are typical coaxial transmission lines, and transmission line theory is usually used to analyze electromagnetic wave transmission problems on them.

In recent years, researchers at home and abroad have applied the frequency domain reflection spectrum detection technology based on transmission line theory to high-voltage cable line fault detection. The frequency domain reflection spectrum detection technology can detect and locate the defects of the buffer layer of high-voltage cables. Among them, the accurate positioning spectrum function must be established for the local defect location of high-voltage cables. The kernel function is crucial and needs to be constructed through the distribution parameters of the high-voltage cable body. The current kernel function acquisition method has a large error, which leads to the inability to obtain accurate results when using the frequency domain reflection spectrum detection technology to detect and locate the defects of the buffer layer of high-voltage cables.

Summary of the invention

The purpose of the present invention is to provide a method, system, device and medium for locating local defects of cables to solve one or more of the above-mentioned technical problems. In the technical solution provided by the present invention, a new method for obtaining a local defect locating kernel function of cables is disclosed, which can obtain an accurate locating kernel function and ultimately improve the locating accuracy of local defects of cables.

In order to achieve the above object, the present invention adopts the following technical solutions:

The present invention provides a method for locating local defects of a cable, comprising the following steps:

The frequency domain reflection spectrum is used to locate the local defects of the cable and obtain the positioning results; among them,

When using frequency domain reflection spectrum to locate local defects of cables, the spectral function F(x) of high-voltage cable local defect location based on the integral transformation method of generalized orthogonal theory is:

Where Z(f) is the frequency domain reflection spectrum of the cable head end; K(f,x) is the kernel function of the positioning spectrum function; _f1 is the upper frequency limit of the frequency domain reflection spectrum; _f2 is the lower frequency limit of the frequency domain reflection spectrum; x is the spatial position of the cable;

The expression of the kernel function is:

K(f,x)＝e ^-2γx ；

Where γ is the propagation constant of the cable body,

In the formula, R is the resistance per unit length of the cable body; L is the inductance per unit length of the cable body; G is the conductance per unit length of the cable body; C is the capacitance per unit length of the cable body;

Among them, the resistance per unit length of the cable body and the inductance per unit length of the cable body are obtained by combining the finite element calculation method and the analytical calculation method; the conductance per unit length of the cable body and the capacitance per unit length of the cable body are obtained by establishing a layered model of the cable insulation medium taking into account the semi-conductive layer.

A further improvement of the present invention is that the step of obtaining the resistance per unit length of the cable body and the inductance per unit length of the cable body by combining a finite element calculation method and an analytical calculation method comprises:

Based on the finite element calculation method, a two-dimensional geometric model of the cable body is established; wherein the two-dimensional geometric model of the cable body includes a center conductor, a conductor shielding layer, an insulating layer, an insulating shielding layer, a buffer layer, a metal shielding layer and an outer sheath, and the material type and material parameters are set according to the types of various structural materials of the cable and the variation rules of the physical parameters of the materials with temperature and frequency;

Performing eddy current field analysis on the obtained two-dimensional geometric model of the cable body; wherein, adding an infinite element domain to the two-dimensional geometric model of the cable body to obtain a two-dimensional finite element model; performing meshing on the obtained two-dimensional finite element model to obtain a meshed two-dimensional finite element simulation model;

The frequency domain solution method is used to calculate and obtain the field solution through the two-dimensional finite element simulation model. The calculated field solution is then converted into the resistance and inductance per unit length of the cable body to obtain the finite element calculation result.

The finite element calculation results are compared with the analytical solutions of the cable body's resistance and inductance per unit length. When the preset error requirements are met, the final cable body's resistance per unit length and the cable body's inductance per unit length are obtained.

A further improvement of the present invention is that the infinite element domain is used to simulate an open surface, and the description expression at the boundary of the infinite element domain is,

In the formula, r is the distance between the source point and the field point; _k0 is the wave number; _Az is the component of the magnetic vector potential on the z-axis; _x1 is the horizontal coordinate of the field point; _y1 is the vertical coordinate of the field point.

A further improvement of the present invention is that when the frequency domain solution method is used for calculation, the frequency of the parametric scan is set to 1 Hz to 100 MHz.

A further improvement of the present invention is characterized in that, in the step of converting the calculated field solution into the resistance and inductance per unit length of the cable body,

The calculation expression of the resistance per unit length of the cable body is:

分别为面s所通过的总电流和电势差；J^*为电流密度矢量的共轭；E为电场强度矢量；In the formula, I ₀ and

are the total current and potential difference passing through surface s respectively; J ^* is the conjugate of the current density vector; E is the electric field intensity vector;

The calculation expression of the inductance per unit length of the cable body is,

Where B is the magnetic induction intensity vector; _Wm is the magnetic field energy; H ^* is the conjugate of the magnetic field intensity vector; _I0 is the total current passing through surface s.

A further improvement of the present invention is that in the step of obtaining the analytical solution of the resistance and inductance per unit length of the cable body,

The expressions of the resistance and inductance per unit length of the cable body are,

其中，R = real (Z _c + Z _s ) and

in,

Wherein, _Zc is the internal impedance per unit length of the central conductor of the cable body; _r1 is the radius of the central conductor; _mc is the inverse of the composite penetration depth of the central conductor; _ρc is the resistivity of the central conductor; _Ac is the nominal cross-sectional area of the central conductor; j is the imaginary unit; _μ3 is the magnetic permeability of the central conductor; ω is the angular frequency; _I0 (x) is the 0th order first-order modified Bessel function; _I1 (x) is the 1st order first-order modified Bessel function; _Zs is the internal impedance per unit length of the metal shielding layer of the cable body; _ms is the inverse of the composite penetration depth of the metal shielding layer; _ρs is the resistivity of the metal shielding layer; _r2 is the inner radius of the metal shielding layer; _r3 is the outer radius of the metal shielding layer; _μ2 is the magnetic permeability of the metal shielding layer; _K0 (x) is the 0th order second-order modified Bessel function; _K1 (x) is the 1st order second-order modified Bessel function; _Le is the external inductance per unit length from the central conductor of the cable body to the metal shielding layer; _μ3 is the magnetic permeability of the insulating material.

A further improvement of the present invention is that the conductance per unit length of the cable body and the capacitance per unit length of the cable body are obtained by establishing a layered model of the cable insulation medium taking into account the semi-conductive layer, comprising:

The admittance per unit length of the cable is the capacitance and conductance of each layer of the insulating medium connected in parallel, and then the admittances of each layer of the insulating medium connected in series;

The unit length capacitance C _k and conductance G _k of the kth insulating medium are respectively:

Where: ε _k is the dielectric constant of the kth insulating medium; σ _k is the conductivity of the kth insulating medium; r _k+1 is the outer radius of the kth insulating medium; r _k is the inner radius of the kth insulating medium;

The unit length admittance _Yk of the kth insulating medium is,

The admittance per unit length Y of the cable containing N layers of insulating medium between the center conductor and the metal shield is,

The conductance per unit length of the cable body and the capacitance per unit length of the cable body are G=Re(Y) and C=Im(Y)/ω respectively.

The present invention provides a cable local defect positioning system, comprising:

The positioning module is used to locate local defects of the cable using the frequency domain reflection spectrum to obtain the positioning results;

When using frequency domain reflection spectrum to locate local defects of cables, the spectral function F(x) of high-voltage cable local defect location based on the integral transformation method of generalized orthogonal theory is:

Where Z(f) is the frequency domain reflection spectrum of the cable head end; K(f,x) is the kernel function of the positioning spectrum function; _f1 is the upper frequency limit of the frequency domain reflection spectrum; _f2 is the lower frequency limit of the frequency domain reflection spectrum; x is the spatial position of the cable;

The expression of the kernel function is:

K(f,x)＝e ^-2γx ；

Where γ is the propagation constant of the cable body,

In the formula, R is the resistance per unit length of the cable body; L is the inductance per unit length of the cable body; G is the conductance per unit length of the cable body; C is the capacitance per unit length of the cable body;

Among them, the resistance per unit length of the cable body and the inductance per unit length of the cable body are obtained by combining the finite element calculation method and the analytical calculation method; the conductance per unit length of the cable body and the capacitance per unit length of the cable body are obtained by establishing a layered model of the cable insulation medium taking into account the semi-conductive layer.

The present invention provides an electronic device, comprising:

at least one processor; and,

a memory communicatively connected to the at least one processor; wherein,

The memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the cable local defect locating method as described above in any one of the present inventions.

The present invention provides a computer-readable storage medium storing a computer program, wherein the computer program, when executed by a processor, implements any one of the above-mentioned methods for locating local defects of a cable of the present invention.

Compared with the prior art, the present invention has the following beneficial effects:

In the cable local defect location method provided by the present invention, the frequency domain reflection spectrum is used to locate the local defects of the cable; wherein, it is necessary to perform the conversion from the frequency domain to the space domain through the integral transformation method based on the generalized orthogonal theory, and establish the location spectrum function; the kernel function plays a decisive role in the location spectrum function. In the technical scheme of the present invention, a new method for obtaining the local defect location kernel function of the cable is disclosed, which can obtain an accurate location kernel function, and finally improve the location accuracy of the local defects of the cable; wherein, the wide frequency domain unit length resistance and inductance of the cable body are calculated by combining the finite element calculation method and the analytical calculation method; the insulating medium structure of the cable is relatively complex, and a layered model of the cable insulating medium considering the semi-conductive layer is established to calculate the wide frequency domain unit length conductance and capacitance of the cable body. In summary, the method of the present invention is of great significance to improving the location accuracy of local defects in the cable and has great engineering value.

In the present invention, the calculation method of the cable unit length resistance and unit length inductance is applicable to high-voltage cables of any voltage level, and is simple to operate and convenient to solve; wherein, the calculation method of the cable unit length resistance and unit length inductance can simultaneously consider the influence of factors such as temperature and frequency on the dielectric parameters of the cable material, and can accurately calculate the wide-frequency unit length resistance and inductance of the high-voltage cable body, thus solving the problem of the calculation accuracy of the wide-frequency unit length resistance and inductance of the high-voltage cable body.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art; obviously, the drawings described below are some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

FIG1 is a schematic diagram of a process for obtaining a kernel function in an embodiment of the present invention;

2 is a schematic diagram of a calculation flow of the resistance per unit length and the inductance per unit length of a high-voltage cable body in an embodiment of the present invention;

FIG3 is a schematic structural diagram of a high voltage cable body in an embodiment of the present invention;

FIG4 is a schematic diagram of grid division of a high-voltage cable body in an embodiment of the present invention;

FIG5 is a schematic diagram of mesh division of an infinite element domain in an embodiment of the present invention;

6 is a schematic diagram showing a comparison between a finite element calculation result and an analytical solution of the resistance per unit length of a high-voltage cable body in an embodiment of the present invention;

7 is a schematic diagram showing a comparison between the finite element calculation results and the analytical solution of the inductance per unit length of the high-voltage cable body in an embodiment of the present invention;

FIG8 is a schematic diagram of an equivalent circuit between a central conductor and a metal shielding layer of a high-voltage cable in an embodiment of the present invention.

DETAILED DESCRIPTION

In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

The present invention is further described in detail below in conjunction with the accompanying drawings:

In the embodiment of the present invention, when using the frequency domain reflection spectrum to locate the local defects of the cable, it is necessary to convert the frequency domain to the spatial domain through the integral transformation method based on the generalized orthogonal theory, and establish a positioning spectrum function; wherein the kernel function plays a decisive role in the positioning spectrum function. In order to improve the positioning accuracy, it is necessary to accurately calculate the distributed electrical parameters of the high-voltage cable in the transmission line model, including the unit length resistance, unit length inductance, unit length conductance and unit length capacitance of the cable body.

The embodiment of the present invention is exemplary. In the calculation of the unit length resistance and inductance of the high-voltage cable body, more analytical algorithms are currently used, taking into account the skin effect of the entire frequency band under wide frequency; however, the current is evenly distributed in the extremely low frequency band, and no skin effect is produced, so there is a large error at low frequency. In addition, the structure of the high-voltage cable body is relatively complex, and it is necessary to consider the influence of factors such as the structure of the high-voltage cable body and the dielectric characteristics of each layer. In particular, the semiconductor layer of the high-voltage cable body has frequency-varying characteristics at high frequencies. When the dielectric properties change, it has a certain influence on the distribution of the magnetic field in the high-voltage cable body, which will affect the accuracy of the analytical calculation results of the unit length resistance and inductance of the high-voltage cable body, and produce certain errors. The finite element calculation method is adopted in the technical solution of this embodiment, which can simultaneously consider the influence of factors such as temperature and frequency on the dielectric parameters of each layer of the cable material, and can efficiently and accurately calculate the complex physical field according to the set conditions. In summary, the embodiment of the present invention establishes a method for accurately calculating the distribution parameters of the high-voltage cable body, and thus can obtain an accurate positioning kernel function.

An embodiment of the present invention provides a method for locating a local defect of a cable, comprising the following steps:

The frequency domain reflection spectrum is used to locate the local defects of the cable and obtain the positioning results. When the frequency domain reflection spectrum is used to locate the local defects of the cable, the high-voltage cable local defect positioning spectrum function F(x) based on the integral transformation method of the generalized orthogonal theory is:

Where Z(f) is the frequency domain reflection spectrum of the cable head end; K(f,x) is the kernel function of the positioning spectrum function; _f1 is the upper frequency limit of the frequency domain reflection spectrum; _f2 is the lower frequency limit of the frequency domain reflection spectrum; x is the spatial position of the cable;

Among them, the kernel function K(f,x) in the cable local defect location spectrum function F(x) is a function of the frequency f and the cable spatial position x, and its expression is:

K(f,x)＝e ^-2γx ；

Where γ is the propagation constant of the cable itself.

In the embodiment of the present invention, the propagation constant γ of the cable body is calculated as follows:

Where R is the resistance per unit length of the cable body; L is the inductance per unit length of the cable body; G is the conductance per unit length of the cable body; C is the capacitance per unit length of the cable body.

Please refer to FIG. 1 . In an embodiment of the present invention, when obtaining the kernel function K(f,x) in the cable local defect location spectrum function F(x), taking the high-voltage cable local defect location as an example, the following steps are specifically included:

Obtain the broadband resistance and inductance per unit length of the high-voltage cable body; obtain the broadband conductance and capacitance per unit length of the high-voltage cable body;

Based on the above-obtained parameters, the propagation constant of the high-voltage cable body is calculated;

Based on the obtained propagation constant of the high-voltage cable body, the kernel function K(f,x) for local defect location of the high-voltage cable is established.

Please refer to FIG. 2 . In the embodiment of the present invention, in the step of obtaining the broadband resistance and inductance per unit length of the high-voltage cable body, the variation law of the physical parameters of each structural material of the high-voltage cable with temperature and frequency is fully considered. The resistance per unit length and the inductance per unit length are calculated by combining the finite element calculation method and the analytical method. The exemplary specific steps include:

Step (1), using a finite element calculation method to establish a two-dimensional geometric model of a high-voltage cable body, the model including a center conductor, a conductor shielding layer, an insulating layer, an insulating shielding layer, a buffer layer, a metal shielding layer and an outer sheath; wherein, in a further specific exemplary manner, the geometric parameters of the high-voltage cable body include an effective cross-sectional area and radius of the center conductor and inner and outer radii of the conductor shielding layer, the insulating layer, the insulating shielding layer, the buffer layer (semiconductor water-resistant tape and metal shielding cloth tape), the metal shielding layer, and the outer sheath;

Step (2), according to the variation of each structural material type and material physical parameters of the high-voltage cable with temperature and frequency, setting material type and material parameters for each layer of the two-dimensional geometric model of the high-voltage cable body; wherein further explaining, the material parameters of the high-voltage cable body include conductivity, relative dielectric constant, relative magnetic permeability and dielectric loss, and also include their variation with temperature and frequency;

Step (3), performing eddy current field analysis on the two-dimensional geometric model of the high-voltage cable body, wherein the central conductor and the metal shielding layer in the eddy current field are used as a coil group, a current of 1A is applied to the central conductor, and a reverse current flows through the metal shielding layer; an infinite element domain is added to the two-dimensional geometric model, and the radius is twice the radius of the cable body, and a two-dimensional finite element model is established; wherein,

Further illustratively, in step (3) of the embodiment of the present invention, the infinite element domain (radiation boundary) is used to extend to an outer boundary infinitely far away, simulating an open surface, that is, waves can radiate in the direction of the radiation boundary; the radiation boundary can be of any shape and close to the model structure; in this way, the solution area becomes a finite area.

At the boundary of the infinite element domain, the magnetic field is neither parallel nor perpendicular to the boundary, which can be described by equations (1) and (2).

In the formula, r is the distance between the source point and the field point; _k0 is the wave number; _Az is the component of the magnetic vector potential on the z-axis; _x1 is the horizontal coordinate of the field point; _y1 is the vertical coordinate of the field point.

Step (4), performing free triangle meshing on the established two-dimensional finite element model to establish a meshed two-dimensional finite element simulation model; wherein, when meshing, it is necessary to add a boundary layer mesh, which is a typical subdivision method in meshing and is particularly suitable for eddy current effects in electromagnetic fields;

Step (5), using the frequency domain solution method, setting the frequency of the parametric scan to 1 Hz to 100 MHz, and performing calculations;

Step (6), after obtaining the field solution through the high-voltage cable finite element model, the calculated field solution is converted into the unit length resistance and inductance of the high-voltage cable body; wherein,

The resistance per unit length of the high-voltage cable body is mainly determined by the current distribution of the central conductor and the metal shielding layer. It can be calculated by integrating the product of current density and electric field strength. According to electromagnetic field theory,

为面s所通过的总电流和电势差；J^*为电流密度矢量的共轭；E为电场强度矢量。In the formula, I ₀ and

is the total current and potential difference passing through surface s; J ^* is the conjugate of the current density vector; E is the electric field strength vector.

Therefore, the calculation formula for unit length resistance R is,

The inductance per unit length of the high-voltage cable is mainly determined by the magnetic field. A circular magnetic field will be generated around the energized cable. The magnetic induction intensity vector of the circular magnetic field is B. The magnetic field energy W _m can be obtained by integrating the magnetic field energy density or the effective value and inductance of the cable center conductor current. The calculation formulas are as follows:

Where H ^* is the conjugate of the magnetic field intensity vector; _I0 is the total current passing through surface s; and L is the inductance per unit length.

Therefore, the calculation formula for the inductance per unit length L is,

Step (7), within 1Hz~10MHz, compare the finite element calculation results with the analytical solution of the resistance and inductance per unit length of the high-voltage cable body. If the relative error between the two is less than 0.05%, the resistance and inductance per unit length of the high-voltage cable body calculated by the finite element is the resistance and inductance per unit length of the high-voltage cable body; if the relative error between the two is greater than 0.05%, re-perform the finite element calculation and repeat steps 4~7 until the error is less than 0.05%, and finally obtain the accurate resistance and inductance per unit length of the high-voltage cable body in the wide frequency domain; wherein,

The analytical solution of the resistance and inductance per unit length of the high-voltage cable body is as follows:

The internal impedance _Zc per unit length of the central conductor of the high-voltage cable body is:

Wherein, _r1 is the radius of the central conductor; _mc is the inverse of the composite penetration depth of the central conductor; _ρc is the resistivity of the central conductor; _Ac is the nominal cross-sectional area of the central conductor; j is the imaginary unit; _μ1 is the magnetic permeability of the central conductor; ω is the angular frequency; _I0 (x) is the 0th order first kind modified Bessel function; _I1 (x) is the 1st order first kind modified Bessel function;

The internal impedance per unit length of the metal shielding layer of the high-voltage cable body is:

Wherein, _ms is the inverse of the composite penetration depth of the metal shielding layer; _ρs is the resistivity of the metal shielding layer; _r2 is the inner radius of the metal shielding layer; _r3 is the outer radius of the metal shielding layer; _μ2 is the magnetic permeability of the metal shielding layer; _K0 (x) is the 0th order modified Bessel function of the second kind; _K1 (x) is the 1st order modified Bessel function of the second kind;

The external inductance _Le per unit length from the central conductor of the high-voltage cable body to the metal shielding layer is:

Where μ ₃ is the magnetic permeability of the insulating material;

From the above formula, the analytical calculation formulas of the unit length resistance R and inductance L of the high-voltage cable body are:

R = real (Z _c + Z _s );

In the embodiment of the present invention, the insulating medium structure of the high-voltage cable is relatively complex. A layered model of the high-voltage cable insulating medium considering the semi-conductive layer is established to calculate the broadband conductance and capacitance per unit length of the high-voltage cable body. The specific process may include:

The admittance per unit length of the high-voltage cable is the capacitance and conductance of each layer of the insulating medium connected in parallel, and then the admittance of each layer of the insulating medium connected in series. The calculation formula is:

The capacitance C _k and conductance G _k per unit length of the kth insulating medium are:

In the formula: ε _k is the dielectric constant of the kth insulating medium; σ _k is the conductivity of the kth insulating medium; r _k+1 is the outer radius of the kth insulating medium; r _k is the inner radius of the kth insulating medium.

The unit length admittance _Yk of the kth insulating medium is:

The unit length admittance Y of the high-voltage cable containing N layers of insulating medium between the central conductor and the metal shield is,

The unit length conductance G and unit length capacitance C of the high voltage cable are respectively,

G = Re (Y);

C＝Im(Y)/ω.

In the embodiment of the present invention, the propagation constant γ of the high-voltage cable body is calculated as follows:

In the formula, R is the resistance per unit length of the high-voltage cable body; L is the inductance per unit length of the high-voltage cable body; G is the conductance per unit length of the high-voltage cable body; C is the capacitance per unit length of the high-voltage cable body.

In the embodiment of the present invention, the spectral function F(x) of the local defect location of the high-voltage cable based on the integral transformation method of the generalized orthogonal theory is:

Where: Z(f) is the frequency domain reflection spectrum of the head end of the high-voltage cable; K(f,x) is the kernel function of the positioning spectrum function; _f1 is the upper frequency limit of the frequency domain reflection spectrum; _f2 is the lower frequency limit of the frequency domain reflection spectrum; x is the spatial position of the high-voltage cable;

The kernel function K(f,x) in the high-voltage cable local defect location spectrum function F(x) is a function of the frequency f and the high-voltage cable spatial position x. It plays a decisive role in the location spectrum function and is expressed as follows:

K(f,x)＝e ^-2γx .

The method for obtaining the kernel function for locating local defects of high-voltage cables provided in an embodiment of the present invention can accurately establish the kernel function in the spectrum function for locating local defects of high-voltage cables, and can improve the positioning accuracy of local defects of high-voltage cables; wherein, the method for calculating the resistance per unit length and the inductance per unit length of high-voltage cables is applicable to high-voltage cables of any voltage level, and is simple to operate and convenient to solve; the method for calculating the resistance per unit length and the inductance per unit length of high-voltage cables can simultaneously consider the influence of factors such as temperature and frequency on the dielectric parameters of cable materials, and can accurately calculate the resistance per unit length and inductance per unit length of the high-voltage cable body in a wide frequency domain, thereby solving the problem of the calculation accuracy of the resistance per unit length and inductance per unit length of the high-voltage cable body in a wide frequency domain.

In an exemplary embodiment of the present invention, the steps of calculating the broadband resistance per unit length and the inductance per unit length of the high-voltage cable body specifically include:

(1) A two-dimensional geometric model of the high-voltage cable body is established, which includes a central conductor, a conductor shielding layer, an insulating layer, an insulating shielding layer, a buffer layer, a metal shielding layer, and an outer sheath; the geometric parameters include the effective cross-sectional area and radius of the central conductor and the inner and outer radii of the conductor shielding layer, the insulating layer, the insulating shielding layer, the buffer layer (semiconductor water-resistant tape and metal shielding cloth tape), the metal shielding layer, and the outer sheath; specifically, the structural schematic diagram of the high-voltage cable body is shown in FIG3 .

(2) According to the variation patterns of the structural material types and material physical parameters of the high-voltage cable with temperature and frequency, the material types and material parameters are set for each layer of the two-dimensional geometric model of the high-voltage cable body. The material parameters of the high-voltage cable body include electrical conductivity, relative dielectric constant, relative magnetic permeability and dielectric loss, as well as their variation patterns with temperature and frequency.

(3) Perform eddy current field analysis on the two-dimensional geometric model of the high-voltage cable body. The central conductor and the metal shielding layer in the eddy current field serve as a coil group. A current of 1A is applied to the central conductor, and a reverse current flows through the metal shielding layer. An infinite element domain is added to the two-dimensional geometric model, and the radius is twice the radius of the cable body, and a two-dimensional finite element model is established. The infinite element domain (radiation boundary) is used to extend to the outer boundary at infinity to simulate an open surface, that is, waves can radiate in the direction of the radiation boundary. The radiation boundary can be of any shape and close to the model structure. In this way, the solution area becomes a finite area. At the boundary of the infinite element domain, the magnetic field is neither parallel nor perpendicular to the boundary, as shown in the formula in the above embodiment.

(4) Perform free triangular meshing on the established two-dimensional finite element model to establish a meshed two-dimensional finite element model; boundary layer meshing needs to be added during meshing, which is a typical subdivision method in meshing and is particularly suitable for eddy current effects in electromagnetic fields; specifically, meshing is shown in FIGS. 4 and 5.

(5) Using the frequency domain solution method, set the frequency of the parametric scan to 1 Hz to 100 MHz and perform the calculation.

(6) After the field solution is calculated by the finite element model of the high-voltage cable, the calculated field solution is converted into the unit length resistance and inductance of the high-voltage cable body. The unit length resistance of the high-voltage cable body is mainly determined by the current distribution of the center conductor and the metal shielding layer, which can be calculated by integrating the product of the current density and the electric field intensity.

The inductance per unit length of the high-voltage cable body is mainly determined by the magnetic field. A circular magnetic field will be generated around the energized cable. The magnetic induction intensity vector of the circular magnetic field is B. The magnetic field energy W _m can be obtained by integrating the magnetic field energy density or the effective value and inductance of the cable center conductor current.

(7) Within 1Hz~10MHz, the finite element calculation results are compared with the analytical solutions of the resistance and inductance per unit length of the high-voltage cable body. If the relative error between the two is less than 0.05%, the resistance and inductance per unit length of the high-voltage cable body calculated by the finite element are the resistance and inductance per unit length of the high-voltage cable body; if the relative error between the two is greater than 0.05%, the finite element calculation is repeated, and steps (4) to (7) are repeated until the error is less than 0.05%, and finally the accurate resistance and inductance per unit length of the high-voltage cable body in the wide frequency domain are obtained. Figures 6 and 7 are the resistance and inductance per unit length of the high-voltage cable body calculated for an example of a 330kV 1× ^2000mm2 high-voltage cable.

The insulating medium structure of high-voltage cables is relatively complex. A layered model of high-voltage cable insulating medium considering the semi-conductive layer is established to calculate the conductance and capacitance per unit length of the high-voltage cable body in the wide frequency domain. The admittance per unit length of the high-voltage cable is the capacitance and conductance of each layer of insulating medium connected in parallel, and then the admittance of each layer of insulating medium connected in series, as shown in Figure 8.

In summary, the technical solution provided by the embodiment of the present invention can accurately calculate the wide-frequency domain unit length resistance, unit length inductance, unit length conductance and unit length capacitance of the high-voltage cable body, thereby obtaining the propagation constant of the high-voltage cable, and can accurately establish the local defect positioning kernel function of the high-voltage cable, which can improve the positioning accuracy of the local defects of the high-voltage cable to a great extent, and has great reference value and important guiding significance for engineering applications. Further specifically explained, the use of frequency domain reflection spectrum to locate the local defects of the high-voltage cable requires the conversion from the frequency domain to the spatial domain through the integral transformation method based on the generalized orthogonal theory, and the establishment of the positioning spectrum function, in which the kernel function K (f, x) plays a decisive role in the positioning spectrum function; the method for obtaining the local defect positioning kernel function of the high-voltage cable proposed in the embodiment of the present invention is of great significance to improving the positioning accuracy of the local defects of the high-voltage cable, and has great engineering value.

The following are device embodiments of the present invention, which can be used to perform method embodiments of the present invention. For details not disclosed in the device embodiments, please refer to the method embodiments of the present invention.

An embodiment of the present invention provides a cable local defect location system, comprising:

The positioning module is used to locate local defects of the cable using the frequency domain reflection spectrum to obtain the positioning results;

When using frequency domain reflection spectrum to locate local defects of cables, the spectral function F(x) of high-voltage cable local defect location based on the integral transformation method of generalized orthogonal theory is:

Where Z(f) is the frequency domain reflection spectrum of the cable head end; K(f,x) is the kernel function of the positioning spectrum function; _f1 is the upper frequency limit of the frequency domain reflection spectrum; _f2 is the lower frequency limit of the frequency domain reflection spectrum; x is the spatial position of the cable;

The expression of the kernel function is:

K(f,x)＝e ^-2γx ；

Where γ is the propagation constant of the cable body,

In the formula, R is the resistance per unit length of the cable body; L is the inductance per unit length of the cable body; G is the conductance per unit length of the cable body; C is the capacitance per unit length of the cable body;

Among them, the resistance per unit length of the cable body and the inductance per unit length of the cable body are obtained by combining the finite element calculation method and the analytical calculation method; the conductance per unit length of the cable body and the capacitance per unit length of the cable body are obtained by establishing a layered model of the cable insulation medium taking into account the semi-conductive layer.

In another embodiment of the present invention, a computer device is provided, the computer device comprising a processor and a memory, the memory is used to store a computer program, the computer program comprises program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc., which are the computing core and control core of the terminal, which are suitable for implementing one or more instructions, and are specifically suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding functions; the processor described in the embodiment of the present invention can be used for the operation of the cable local defect location method.

In another embodiment of the present invention, the present invention further provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It is understandable that the computer-readable storage medium here can include both built-in storage media in the computer device and, of course, extended storage media supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the cable local defect location method in the above embodiment.

Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

The present application is described with reference to the flowchart and/or block diagram of the method, device (system) and computer program product according to the embodiment of the present application. It should be understood that each process and/or box in the flowchart and/or block diagram, and the combination of the process and/or box in the flowchart and/or block diagram can be realized by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device produce a device for realizing the function specified in one process or multiple processes in the flowchart and/or one box or multiple boxes in the block diagram.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory produce a manufactured product including an instruction device that implements the functions specified in one or more processes in the flowchart and/or one or more boxes in the block diagram.

These computer program instructions may also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more processes in the flowchart and/or one or more boxes in the block diagram.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims (10)

1. The cable local defect positioning method is characterized by comprising the following steps of:

positioning the local defects of the cable by using the frequency domain reflection spectrum to obtain a positioning result; wherein,

when the frequency domain reflection spectrum is used for positioning the local defects of the cable, the function F (x) of the positioning spectrum of the local defects of the high-voltage cable based on the integral transformation method of the generalized orthogonal theory is,

wherein Z (f) is the frequency domain reflection spectrum of the head end of the cable; k (f, x) is a kernel function of the location spectrum function; f (f) ₁ The upper frequency limit of the frequency domain reflection spectrum; f (f) ₂ A lower frequency limit for the frequency domain reflection spectrum; x is the cable space position;

the expression of the kernel function is that,

K(f,x)＝e ^-2γx ；

where gamma is the propagation constant of the cable body,

wherein R is the resistance per unit length of the cable body; l is inductance per unit length of the cable body; g is the conductance per unit length of the cable body; c is the capacitance per unit length of the cable body;

the resistance per unit length of the cable body and the inductance per unit length of the cable body are obtained through a mode of combining a finite element calculation method and an analytic calculation method; the conductance per unit length of the cable body and the capacitance per unit length of the cable body are obtained by establishing a layering model of the cable insulation medium taking the semiconductive layer into consideration.

2. The method of claim 1, wherein the step of obtaining the resistance per unit length of the cable body and the inductance per unit length of the cable body by a combination of a finite element calculation method and a analytic calculation method comprises:

based on a finite element calculation method, establishing and acquiring a two-dimensional geometric model of the cable body; the cable body two-dimensional geometric model comprises a central conductor, a conductor shielding layer, an insulating shielding layer, a buffer layer, a metal shielding layer and an outer sheath, and material types and material parameters are arranged according to the change rule of each structural material type and material physical parameter of the cable along with temperature and frequency;

carrying out vortex field analysis on the obtained two-dimensional geometric model of the cable body; adding an infinite element domain to the two-dimensional geometric model of the cable body to obtain a two-dimensional finite element model; performing mesh subdivision on the obtained two-dimensional finite element model to obtain a two-dimensional finite element simulation model of mesh subdivision;

calculating by using a frequency domain solving method, obtaining a field solution by calculating through a two-dimensional finite element simulation model, and then converting the field solution obtained by calculation into a resistance and an inductance of a cable body in unit length to obtain a finite element calculation result;

Comparing the finite element calculation result with the analysis solution of the resistance and the inductance of the unit length of the cable body, and obtaining the final resistance and the inductance of the unit length of the cable body when the analysis solution meets the preset error requirement.

3. The method of claim 2, wherein the infinite field is used to simulate an open surface, the descriptive expression at the boundary of the infinite field being,

wherein r is the distance between the source point and the field point; k (k) ₀ Is wave number; a is that _z Is the component of the magnetic vector in the z-axis; x is x ₁ Is the abscissa of the field point; y is ₁ Is the ordinate of the field point.

4. The method of claim 2, wherein the frequency of the parametric sweep is set to 1Hz to 100MHz when the calculation is performed using a frequency domain solving method.

5. The method of claim 2, wherein in the step of converting the calculated field solution into a resistance per unit length and an inductance of the cable body,

the calculated expression of the resistance per unit length of the cable body is,

in the formula ,I₀ And

the total current and potential difference through the face s, respectively; j (J) ^* Is the conjugation of the current density vector; e is the electric field intensity vector;

the calculated expression of the inductance per unit length of the cable body is,

Wherein B is a magnetic induction intensity vector; w (W) _m Is the magnetic field energy; h ^* Is the conjugation of the magnetic field intensity vector; i ₀ Is the total current through the face s.

6. The method according to claim 2, wherein in the step of obtaining the analytical solution of the resistance and inductance of the unit length of the cable body,

the expressions of the resistance and the inductance of the unit length of the cable body are respectively,

R＝real(Z _c +Z _s) and

wherein ,

in the formula ,Z_c The internal impedance of the central conductor unit length of the cable body; r is (r) ₁ Is the radius of the center conductor; m is m _c The reciprocal of the composite penetration depth of the center conductor; ρ _c Resistivity for the center conductor; a is that _c Is the nominal cross-sectional area of the center conductor; j is an imaginary unit; mu (mu) ₃ Magnetic permeability for the center conductor; omega is the angular frequency; i ₀ (x) Correcting the Bessel function for the first class of 0 th order; i ₁ (x) Correcting the Bessel function for the first class of 1; z is Z _s The inner impedance of the unit length of the metal shielding layer of the cable body is; m is m _s The reciprocal of the composite penetration depth of the metal shielding layer; ρ _s Is the resistivity of the metal shielding layer; r is (r) ₂ Is the inner radius of the metal shielding layer; r is (r) ₃ Is the outer radius of the metal shielding layer; mu (mu) ₂ Is the magnetic permeability of the metal shielding layer; k (K) ₀ (x) Correcting the Bessel function for the 0 th order second class; k (K) ₁ (x) Correcting the Bessel function for the first class of the first order; l (L) _e An external inductance per unit length from the central conductor of the cable body to the metal shielding layer; mu (mu) ₃ Is the magnetic permeability of the insulating material.

7. The method of claim 1, wherein the step of obtaining the conductance per unit length of the cable body and the capacitance per unit length of the cable body by creating a layered model of the cable insulation medium taking into account the semiconductive layer comprises:

the admittance of the unit length of the cable is that the capacitance and the conductance of each layer of insulating medium are firstly connected in parallel, and then the admittances of all layers of insulating medium are connected in series; wherein,

capacitance C per unit length of k-th layer insulating medium _k And conductance G _k The two kinds of the materials are respectively that,

in the formula ：ε_k A dielectric constant of the k-th insulating medium; sigma (sigma) _k Conductivity of the k-th insulating medium; r is (r) _k+1 An outer radius of the k-th insulating medium; r is (r) _k Is the inner radius of the k-th insulating medium;

admittance per unit length Y of k-th layer insulating medium _k In order to achieve this, the first and second,

admittance Y per unit length of the insulating medium containing N layers between the cable central conductor and the metal shielding layer is,

the conductance per unit length of the cable body and the capacitance per unit length of the cable body are g=re (Y) and c=im (Y) ω, respectively.

8. A cable local defect localization system, comprising:

the positioning module is used for positioning the local defects of the cable by using the frequency domain reflection spectrum to obtain a positioning result; wherein,

When the frequency domain reflection spectrum is used for positioning the local defects of the cable, the function F (x) of the positioning spectrum of the local defects of the high-voltage cable based on the integral transformation method of the generalized orthogonal theory is,

wherein Z (f) is the frequency domain reflection spectrum of the head end of the cable; k (f, x) is a kernel function of the location spectrum function; f (f) ₁ The upper frequency limit of the frequency domain reflection spectrum; f (f) ₂ A lower frequency limit for the frequency domain reflection spectrum; x is the cable space position;

the expression of the kernel function is that,

K(f,x)＝e ^-2γx ；

where gamma is the propagation constant of the cable body,

wherein R is the resistance per unit length of the cable body; l is inductance per unit length of the cable body; g is the conductance per unit length of the cable body; c is the capacitance per unit length of the cable body;

the resistance per unit length of the cable body and the inductance per unit length of the cable body are obtained through a mode of combining a finite element calculation method and an analytic calculation method; the conductance per unit length of the cable body and the capacitance per unit length of the cable body are obtained by establishing a layering model of the cable insulation medium taking the semiconductive layer into consideration.

9. An electronic device, comprising:

at least one processor; the method comprises the steps of,

a memory communicatively coupled to the at least one processor; wherein,

The memory stores instructions executable by the at least one processor to enable the at least one processor to perform the cable partial defect localization method of any one of claims 1-7.

10. A computer readable storage medium storing a computer program, characterized in that the computer program, when executed by a processor, implements the cable local defect localization method according to any one of claims 1 to 7.

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